1. Field of the Invention
The present invention relates to a ramp load type magnetic disk unit and more particularly to a magnetic disk unit suited for disposing of worn particles on a runway of a ramp.
2. Description of the Related Art
A contact start stop (CSS) system is still a commonly used technique of handling a slider when the magnetic disk unit is stopped or started. That is, the slider mounting the magnetic head rests in contact with the surface of the magnetic disk while the unit is stopped. When it is started and the magnetic disk begins to rotate, the slider slides on the surface of the magnetic disk and, when the disk rotation exceeds a predetermined speed, floats over the disk and remains in a steady state. In the stopping process, as the rotation speed of the disk lowers, the slider comes into contact with and slides on the surface of the disk until it stops and rests on the disk.
To prevent the slider from sticking to the magnetic disk, both having smooth surfaces, the CSS system has the surface of the magnetic disk formed with slight undulations (texture surface processing). To improve the recording density, however, the floating distance of the slider from the disk must be minimized, which necessitates the surface of the disk to be formed smoother. Therefore, the undulations on the magnetic disk surface can no longer be tolerated.
A load/unload system is advantageous in this respect. In this system, while magnetic disk unit is stopped, the slider is retracted from the magnetic disk surface. When the magnetic disk rotation reaches a normal speed, the slider is loaded from the retracted or standby position onto the disk surface. When the unit is to be stopped, the slider is unloaded to the standby position before the disk rotation speed is lowered.
With this system, because the slider is not in contact with the disk surface while at rest, there is no need to provide the disk surface with undulations. This is advantageous in reducing the floating distance and increasing the recording density. Of the load/unload system, a ramp load system is simplest in structure and most feasible.
This system has a ramp, a member with a runway, which has an inclined portion near the outermost or innermost periphery of the magnetic disk. During the load/unload operation, a part of the suspension supporting the slider moves up or down the ramp to load/unload the slider.
An example of the ramp load system is the one disclosed in Japanese Patent Laid-Open No. 8-263946. In this conventional technology, a raised spherical member is provided where the suspension slides on the ramp.
In DCTA-24090 (Travelstar 4GT) and DPLA-25120 (Travelstar 5GS), recently commercialized by IBM, a slide portion that slides on the ramp is a dimple shaped like a raised bottom of a boat which is formed by extending one spherical member. The longitudinal direction of the slide portion is arranged perpendicular to the direction of its movement.
The ramp and the slide tab wear out as they are subjected to repetitive compressive and shearing stresses from pressing loads and frictional forces. Particles produced by the wear adhere to the ramp and the slide tab. When the load/unload operation is performed with the particles attached to the ramp and slide tab, the worn particles are very likely to fall on the magnetic disk and be trapped between the slider and the disk, causing unrecoverable damage to the unit as a whole.
Japanese Patent Laid-Open No. 5-166322 discloses a structure that has a projection in the ramp inclined portion to control the speed of the slider landing on the ramp. Although the particles adhering to the slide tab are scraped off by the projection, because the inclined portion is located near the magnetic disk, the particles thus scrapped off are very likely to fall onto the disk. At the inclined portion the sliding speed cannot be set close to zero and the contact stress at the projection is large, so that the wear of the projection will increase the unwanted particles.